The fibrous tissue is made up of a protein called "collagen". At a molecular level the protein consists of three amino acid chains wound together in a tri-helical formation. The molecules have a tendency to line up end to end and to aggregate into larger macro-molecules called "fibrils" and these, in turn, join up and twist together with others to form fibers and ultimately the fiber bundles which can be seen by the naked eye. The unique physical properties of leather come from the way in which these fiber bundles are woven together into a three dimensional network which extends throughout the bulk of the skin.

Here the fiber bundles are large and strong. They lie at varying angles to the grain layer above. This
angle varies in different animals. This angle is known as the 'angle of weave' and it effects the physical properties of the leather. A lower angle of weave produces a softer, weaker and less elastic leather.

In the leather tanning process, an important process called "Fat-liquoring", in this process it uses fats and oils to lubricate and soften the fiber structure of leather. The manner in which the oils are introduced into the hide coat every fiber. This is where leather gets its smell!